package com.store.app.utils;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

public class RandomGUID {
		  
		   public String valueBeforeMD5 = "";  
		   public String valueAfterMD5 = "";  
		   private static Random myRand;  
		   private static SecureRandom mySecureRand;  
		  
		   private static String s_id;  
		   private static final int PAD_BELOW = 0x10;  
		   private static final int TWO_BYTES = 0xFF;  
		  
		   /* 
		    * Static block to take care of one time secureRandom seed. 
		    * It takes a few seconds to initialize SecureRandom.  You might 
		    * want to consider removing this static block or replacing 
		    * it with a "time since first loaded" seed to reduce this time. 
		    * This block will run only once per JVM instance. 
		      */  
		  
		   static {  
		      mySecureRand = new SecureRandom();  
		      long secureInitializer = mySecureRand.nextLong();  
		      myRand = new Random(secureInitializer);  
		      try {  
		         s_id = InetAddress.getLocalHost().toString();  
		      } catch (UnknownHostException e) {  
		         e.printStackTrace();  
		      }  
		  
		   }  
		  
		  
		   /* 
		    * Default constructor.  With no specification of security option, 
		    * this constructor defaults to lower security, high performance. 
		    */  
		   public RandomGUID() {  
		      getRandomGUID(false);  
		   }  
		  
		   /* 
		    * Constructor with security option.  Setting secure true 
		    * enables each random number generated to be cryptographically 
		    * strong.  Secure false defaults to the standard Random function seeded 
		    * with a single cryptographically strong random number. 
		    */  
		   public RandomGUID(boolean secure) {  
		      getRandomGUID(secure);  
		   }  
		  
		   /* 
		    * Method to generate the random GUID 
		    */  
		   private void getRandomGUID(boolean secure) {  
		      MessageDigest md5 = null;  
		      StringBuffer sbValueBeforeMD5 = new StringBuffer(128);  
		  
		      try {  
		         md5 = MessageDigest.getInstance("MD5");  
		      } catch (NoSuchAlgorithmException e) {  
		         e.printStackTrace();
		      }  
		  
		      try {  
		         long time = System.currentTimeMillis();  
		         long rand = 0;  
		  
		         if (secure) {  
		            rand = mySecureRand.nextLong();  
		         } else {  
		            rand = myRand.nextLong();  
		         }  
		         sbValueBeforeMD5.append(s_id);  
		         sbValueBeforeMD5.append(":");  
		         sbValueBeforeMD5.append(Long.toString(time));  
		         sbValueBeforeMD5.append(":");  
		         sbValueBeforeMD5.append(Long.toString(rand));  
		  
		         valueBeforeMD5 = sbValueBeforeMD5.toString();  
		         md5.update(valueBeforeMD5.getBytes());  
		  
		         byte[] array = md5.digest();  
		         StringBuffer sb = new StringBuffer(32);  
		         for (int j = 0; j < array.length; ++j) {  
		            int b = array[j] & TWO_BYTES;  
		            if (b < PAD_BELOW)  
		               sb.append('0');  
		            sb.append(Integer.toHexString(b));  
		         }  
		  
		         valueAfterMD5 = sb.toString();  
		  
		      } catch (Exception e) {  
		         e.printStackTrace();
		      }  
		   }  
		  
		   /* 
		    * Convert to the standard format for GUID 
		    * (Useful for SQL Server UniqueIdentifiers, etc.) 
		    * Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6 
		    */  
		   public String toString() {  
		      String raw = valueAfterMD5.toUpperCase();  
		      StringBuffer sb = new StringBuffer(64);  
		      sb.append(raw.substring(0, 8));  
		      sb.append("-");  
		      sb.append(raw.substring(8, 12));  
		      sb.append("-");  
		      sb.append(raw.substring(12, 16));  
		      sb.append("-");  
		      sb.append(raw.substring(16, 20));  
		      sb.append("-");  
		      sb.append(raw.substring(20));  
		  
		      return sb.toString();  
		   }  
		  
}
